In U.S. Pat. No. 3,879,293, a membrane diffusion device is disclosed having an inflatable member for pressurization and sealing. The inflatable member is U-shaped, to be positioned about the major faces and the bottom side of a stack of membrane sections separated by membrane support member means, and defining interleaving flow paths for two different fluids, separated by the membranes.
The purpose of an inflatable member, whether a flat member as is well-known in the prior art, or the U-shaped member of the above patent, is to selectively apply pressure to the membrane stack by inflation while the stack is retained in a rigid casing, to prevent undue spreading of the fluid paths in the stack when pressurized fluid is provided. This is particularly important in the case where the device is intended for use as a blood oxygenator, an artificial kidney, or the like.
In certain membrane diffusion device constructions, particularly in blood oxygenators, a seal formed from room temperature vulcanizing silicone elastomer is provided between the sides of the membrane blood envelope. The present invention provides means for compressing the end portions of the stack, at the location of the room temperature vulcanizing seal, to prevent or correct leakage problems. By using an external compression system as described herein, the membrane diffusion device casing is strengthened, the end portions of the stack of membrane sections separated by membrane support member means are supported and mechanical support is added to augment the adhesive bonds of the stack.
The external compression means of the present invention is effective to aid in centering the stack in the casing and to constantly and uniformly compress the ends of the stack in a manner which eliminates any non-uniformity of compression of the stack, which may take place when the membrane stack is inserted in a casing having walls that are slightly non-parallel. This helps to reinforce the end seal of the membrane stack, placing a constant compression upon the seal element to prevent seal failure.
An important aspect of the present invention is that the external compression means described herein may be utilized to provide the desired compression to already existing membrane diffusion devices which lack the compressing means described herein.
Other objects and advantages of the present invention will be apparent as the description proceeds.